sorting - I have an issue with implementing Merge Sort for Java -

public static void main(string[] args) {     int[] test = {5,4,3,5,7,5,1,5,96};     system.out.print("before: ");     printlist(test);     mergesort(test, 1, test.length);     //system.out.print("after:  ");     //printlist(test); }  public static void printlist(int[] test){     (int i= 0; < test.length; i++){         system.out.print(test[i] + " ");     }     system.out.println(); }  public static void merge(int[] a, int p, int q, int r){     int n1 = q - p + 1;     int n2 = r - q;      int[] l = new int[n1];     int[] r = new int[n2];      for(int = 1; <= n1; i++){         l[i] = a[p+i-1];     }     (int j = 1; j <= n2; j++){         r[j] = a[q+j];     }     int = 1;     int j = 1;      (int k=p; <= r; i++){         if (i > n1){             a[k] = r[j];             j++;         }         else if (j > n2){             a[k] = l[i];             i++;         }         else if (l[i] <= r[j]){             a[k] = l[i];             i++;         }         else{             a[k] = r[j];             j++;         }     } }  public static void mergesort(int[] a, int p, int r){     if (p < r){         int q = (p + r) / 2;         mergesort(a, p, q);         mergesort(a, q+1, r);         merge(a, p, q, r);     } } 

i trying implement merge sort on test array, not sure why getting arrayindexoutofboundsexception error on this. assignment change merge sort code not use sentinels when searching.

    before: 5 4 3 5 7 5 1 5 96      exception in thread "main" java.lang.arrayindexoutofboundsexception: 1     @ lab1_2.merge(lab1_2.java:28)     @ lab1_2.mergesort(lab1_2.java:61)     @ lab1_2.mergesort(lab1_2.java:59)     @ lab1_2.mergesort(lab1_2.java:59)     @ lab1_2.mergesort(lab1_2.java:59)     @ lab1_2.main(lab1_2.java:8) 

this error message get.

you getting arrayindexoutofboundsexception run time exception because try accessing array out of array boundary (limits). in merge method statements

 int[] l = new int[n1]; 

you declare array of size n1 can element @ index 0 n-1. try storing element @ index n1. not possible because know array having element 0 size-1 (here size length of array) 1 of reason. have issue other places. edit code , hope following code work you.

/* package whatever; // don't place package name! */  import java.util.*;  import java.lang.*;  import java.io.*;   class ideone     {     public static void main (string[] args) throws java.lang.exception     {     // code goes here         int[] test = {5,4,3,5,7,5,1,5,96};     system.out.print("before: ");     printlist(test);     mergesort(test, 0, test.length-1);     system.out.print("after:  ");     printlist(test); }  public static void printlist(int[] test){ (int i= 0; < test.length; i++){     system.out.print(test[i] + " "); } system.out.println(); }  public static void merge(int[] a, int p, int q, int r){ int n1 = q - p + 1; int n2 = r - q;  int[] l = new int[n1]; int[] r = new int[n2];  for(int = 0; < n1; i++){     l[i] = a[p+i]; } (int j = 0; j < n2; j++){     r[j] = a[q+j+1]; } //int = 0; //int j = 0;     /* (int k=p; <= r; i++){     if (i > n1){         a[k] = r[j];         j++;     }     else if (j > n2){         a[k] = l[i];         i++;     }     else if (l[i] <= r[j]){         a[k] = l[i];         i++;     }     else{         a[k] = r[j];         j++;     }     }*/         int = 0, j = 0;       int k = p;     while (i < n1 && j < n2)     {         if (l[i] <= r[j])         {             a[k] = l[i];             i++;         }         else         {             a[k] = r[j];             j++;         }         k++;     }       while (i < n1)     {         a[k] = l[i];         i++;         k++;     }       while (j < n2)     {         a[k] = r[j];         j++;         k++;     }  }  public static void mergesort(int[] a, int p, int r){ if (p < r){     int q = (p + r) / 2;     mergesort(a, p, q);     mergesort(a, q+1, r);     merge(a, p, q, r); } }  }